Mechanisms and pore properties of eco-friendly alkali-activated foam materials prepared with ilmenite tailings and metakaolin

This study demonstrates the first incorporation of ilmenite tailings (IT) into metakaolin (MK)-based alkali-activated foam materials (ITMK-AAFMs), creating lightweight, thermally insulating composites. Foams were synthesized using H₂O₂ (hydrogen peroxide) as a foaming agent and CTAB (cetyltrimethylammonium bromide) as a stabilizer in a sodium hydroxide–sodium silicate activator system. The influence of IT content, liquid-to-solid ratio, and foaming agent dosage on pore structure and thermal properties was systematically investigated. The resulting ITMK-AAFMs exhibited a highly interconnected multiscale (nano- to macro-scale) pore structure with overall porosity up to 73 %. Mechanical testing showed that these ultra-light foams maintained robust strength, with compressive strength reaching 1.20 MPa at a low bulk density of 0.90 g/cm³ . Collectively, the optimized ITMK-AAFMs achieved 99 % pore connectivity, 73.3 % porosity, compressive strength up to 1.20 MPa (at 0.90 g/cm³), and thermal conductivity down to 0.0518 W/m·K, demonstrating a balance of structural robustness and high insulation performance. Increasing the IT content from 0 % to 20 % refined the pore architecture, reducing both the average and modal pore sizes, and enhancing the uniformity of pore distribution. These structural optimizations contributed to exceptionally low thermal conductivity – measured as low as 0.0518 W/m·K in the highest-porosity samples. Thermogravimetric analysis indicated outstanding thermal stability: specimens with 10 % IT experienced minimal mass loss (<2 %) and the smoothest heat-flow transitions upon heating, compared to tailings-free foams. Furthermore, a fractal-based model was developed to predict the thermal conductivity of these porous composites based on their pore structure. This model captured the observed dependence of thermal conductivity on porosity and connectivity. Overall, these findings highlight the potential of ITMK-AAFMs as sustainable construction insulation materials, where controlled inclusion of industrial tailings enhances pore connectivity, mechanical integrity, and thermal performance.